Shdggsdv

I'm trying to fix my performance issues and ran into another question.

I pulled my spark plugs after my missfiring started up again and they were all fouled.. except one. Sparkplug #8 was clean and looked just as it should, but the rest were completely black with a huge layer of carbon (Still trying to figure out what causes me to run so rich). I tried searching for this, but am not coming up with anything.

What, if anything, would this indicate? I've never heard of just a single spark plug being fine while the rest are completely fuel fouled

Not sure if this effects anything, but I rebuilt my carb several weeks ago. My engine was rebuilt less than 10,000 miles ago, but about 10 years ago.

Jud Chapin

Do you do a lot of short trips? If so, this can be your problem due to the choke being on constantly.

Shdggsdv

Lately that's all I've been able to do, but I've already checked and the choke opens and closes just as it should.

Jud Chapin

That's not the point. The choke is supposed to stay on for a while with a cold engine to keep it running smoothly. Change the plugs and stop the short trips as this can do more damage than foul out plugs. When the engine is not completely warmed up, condensation can form inside the engine and exhaust system and take its toll on both.

gungatim

maybe #8 plug was not firing and the source of your misfire. was it wet at all? look like brand new?

MelWff

1. what engine do you have?
2. What brand and part# plug are you using?
3. What carburetor do you have?
4. When you rebuilt it did you correctly adjust the float level?
5. What spark plug gap are you using?
6. Have you checked the spark plug wire resistance?

Shdggsdv

Looks like brand new. The rest are blackened by dry soot. How would I tell if it's not firing? It does look to have a small amount of carbon on the tip of the spark plug so I think it's firing, but I imagine that would mean that that single cylinder is running lean compared to the others?

Shdggsdv

1. Chevy 350 pulled and rebuilt out of a C/K from 1991. Has 305 heads bored to 64cc. Unknown crank and cam, but is probably not too radical as I get 18" of vacuum at idle no problem.

2. AC Delco CR45TS

3. Holley 650cfm 4150 4777-1

4. Yes. Plus, floats were already in decent range of the correct placement.

5. .045 is the gap I'm using

6. I have not tested resistance, but the plugs are "brand new" CarQuest plugs for, I believe, a late 80's Mustang. (I deal with parts, and I pulled these out of our old stock. Probably 8 years old)

Kacyc3

Just because they are brand new doesn't mean they can't be bad, I have seen it before.
You didn't mention how new the cap,rotor, coil and wires are or if you have checked them for arcing traces.

MotorHead

Couple of ways to tell if the #8 plug is not firing. Start it up for a couple of minutes and check the temp of the #8 exhaust tube compared to the others.

Take the plug wire off and see if it runs the same ( bad plug ) or if it runs worse then the plug is good.

I actually installed new plugs and one of them was dead out of the box

CiCiC3

I've had exactly the same trouble with my 454 ever since making a lot performance improvements. My No. 7 stays clean in fact it's running mostly too hot. They all mostly clean up real good after I've taken it for a 10 mile run on the freeway. My carb is obviously running rich but getting it fine tuned without getting it dyno'ed is really tricky. I only drive it a few times a week mostly short distance and that doesn't help. I think my problem is all carburetor related but I just clean the plugs and slap them back in as I don't want to fork out for a dyno. I'm waiting to convert to a Holley EFI next year some time is the master plan in theory. Try getting the engine nice and hot on the freeway for a distance and then check the plugs.

carretera

My #5 and #6 were clean, it pointed to a vacuum leak, traced it to the power booster, first tested booster to see if it held vacuum and it seemed to be ok then I plugged carb vacuum intake bypassing power booster and drove the car and it ran good, replaced the power booster and it runs good now, even burn on all plugs.
The reason I checked the plugs is because car had a bad miss, I must agree a lot of problems with our cars is the lack of driving them, Tony.